Rotate a branch in a tree so that the locations of two bundles of leaves are flipped.

`flip_leaves(dend, leaves1, leaves2, ...)`

- dend
a dendrogram object

- leaves1
a vector of leaves order value to flip.

- leaves2
a (second) vector of leaves order value to flip.

- ...
not used

A dendrogram object with flipped leaves.

This function is based on a bunch of string manipulation functions. There may be a smarter/better way for doing it...

```
if (FALSE) {
dend1 <- USArrests[1:5, ] %>%
dist() %>%
hclust() %>%
as.dendrogram()
dend2 <- flip_leaves(dend1, c(3, 5), c(1, 2))
tanglegram(dend1, dend2)
entanglement(dend1, dend2, L = 2) # 0.4
}
```